1. Field of the Invention
The present invention relates to a press angle control device for a press machine facility provided with a plurality of press machines constituting a press line. Also, the present invention relates to a press machine facility provided with the press angle control device. Also, the present invention relates to a press angle control method for the press machine facility.
2. Description of the Related Art
In the past, a plurality of press machines constitutes a press line in which a plurality of pressing processes is carried out. At this time, a press angle control is carried out so that a press angle difference between the press machines is uniformly maintained or press angles of the press machines are synchronized with each other. A method and a device for performing the press angle control are disclosed in, for example, Japanese Patent No. 3682373 ‘SYNCHRONOUS CONTROL METHOD OF A PLURALITY OF PRESS MACHINES’ and Japanese Laid-open Patent Publication No. 2005-52855 ‘CONTROLLER FOR CONTINUOUS RUNNING OF MECHANICAL DRIVE TYPE TANDEM PRESS LINE’.
In the press angle control disclosed in Japanese Patent No. 3682373, on the basis of a difference between a press angle of a master press machine as a synchronization reference and a press angle of a slave press machine as a synchronization object, a correction amount of a command speed value input to a motor of the slave press machine is obtained, and the correction amount is added to the command speed value input to the motor, thereby synchronizing the press angles with each other.
In the press angle control disclosed in Japanese Laid-open Patent Publication No. 2005-52855, on the basis of a press angle of an upstream press machine, an angle command signal input to a downstream press machine is corrected, thereby performing a phase difference control in which a phase difference between the upstream press machine and the downstream press machine is uniformly maintained.
However, in the press angle control disclosed in Japanese Patent No. 3682373, since the press angle synchronization control is carried out on the basis of the press angle of the master press machine as a synchronization reference in order to synchronize the press angles with each other, when an actual motor speed of the master press machine varies due to a press load increasing during a pressing process, the variation acts on the slave press machine. As a result, a press angle difference occurs between the press machines, and thus a problem arises in that a large error may occur during the press angle control.
Also, in the press angle control disclosed in Japanese Laid-open Patent Publication No. 2005-52855, since the phase difference control is carried out on the basis of the upstream press machine as a reference in order to uniformly maintain the press angle difference between the plurality of press machines, when an actual motor speed of the upstream press machine varies due to a press load increasing during the pressing process, the variation acts on the downstream press machine. As a result, although it is necessary to uniformly maintain the press angle difference, the press angle difference largely varies, and thus a problem arises in that a large error may occur during the press angle control.
Therefore, an object of the invention is to provide a press angle control device, a press machine facility, and a press angle control method capable of reducing a press angle control error caused by a press load variation and of preventing a press load variation of one press machine from acting on the other press machine.